Tag: halo

For this, the last day of the US Fiscal Year, here’s a lovely time lapse video from Tadas Janušonis, a photographer in Lithuania. It’s called "All is Violent, All is Bright", and features a series of interesting optical phenomena in the sky.

He just sent me two more he took last night. He went to Yellowknife, in the Northwest Territories of Canada. The aurorae were active last night as the Sun’s recent hissy fit sparked a geomagnetic storm, but by the time Dave go his equipment set up, the Moon was up and the aurorae fading. But never one to waste an opportunity, he took this incredibly dramatic and moving picture:

Stunning. [Click to enannulenate.] Ice crystals suspended in the air refract (bend) light from the Moon, and due to their geometry they create a ring around it. This is common in winter, but it’s rare — at least in the lower 48 — to get one this bright. The bright "star" on the edge of the ring at the top is actually Mars, which is terribly bright and ruddy in the night skies right now. The fainter star inside the halo is Denebola, the tail of Leo.

He also took this more upbeat picture (click to embiggen) which is another fantastic shot of the halo. You can still see Mars, with the bright Regulus (the heart of Leo) to the right, and just to the left of his hand is either Saturn or the bright blue star Spica in Virgo; I’m not sure which since they’re close to each other in the sky right now. Given how far it’s outside the halo, I’m leaning toward it being Saturn with his hand blocking the view of Spica. As an added bonus, you can see a faint arc of light at the top of the halo, called an upper tangent arc; these are more rare. I’ve only seen them a handful of times near the Sun, and never from a Moon halo!

Having spent a lot of time — a lot — out in the cold waiting for that one great shot, that one great view through the telescope, I can sympathize with what Dave went through to get these… and know he agrees that it was absolutely worth it.

Last night, my in-laws came over for dinner. As I was helping them take leftovers out to their car around 9:00, I do what I always do when I walk outside at night: I looked up.

And man oh man, am I glad I did. Because this is what I saw:

Wow! [Click to refractenate.]

As soon as I saw this, I ran back inside, grabbed my camera, and took this shot. The bright blob in the middle is the Moon — it was just past half full. The "star" to the left is Jupiter, now shining brightly in the east shortly after sunset (the blue and green patches are reflections of the bright Moon inside the camera). You can also see a couple of stars in the constellation Aries just above Jupiter. But dominating the sky was the bright ring around the Moon, called the 22° halo.

Halos like this are caused by ice crystals suspended in the air. The crystals are hexagonal, and light entering one face of the hexagon gets slightly bent, and then bent again as it comes out. The total angle of bending is (at least) 22°, and this is what forms the ring 22° in radius.

Different colors are bent by different amounts; red is bent slightly less than blue, so the inner edge of the halo is red (look at the picture carefully and you’ll see that’s true). The inside of the halo is slightly darker than the sky around it, because no light is bent less than 22°. Light coming to you from the Moon inside that 22° limit gets bent away from you, so you don’t see it. Light outside that limit gets bent toward you, making the bright ring. The halo is actually pretty broad, but fades rapidly outside 23 or so degrees from the Moon, so it looks like a halo. In reality it’s more like a disk with a hole in it.

I love how Jupiter is sitting just outside the ring; in a couple of days the Moon will swing past the giant planet in our sky, missing it by just about 4° (roughly 8 times the size of the Moon’s disk itself). That’ll be a lovely sight.

The picture above was a ten second exposure at f/2.8 and an ISO of 400. Those are standard settings, so it can be pretty easy to take dramatic pictures of the night sky… when the subject is this beautiful.

I’ve seen halos many, many times — though this one was really spectacular. Still, the reason I’ve seen so many is quite simple: I look up. Seriously, that’s all it takes. What glories of nature are you missing by not looking around you?

The footage is from a webcam mounted outside the CFHT astronomical observatory in Hawaii (another view of it from a different webcam can be found here; sadly, both webcams are on Mauna Kea, not Haleakala). You see some stars and the horizon, then suddenly an ethereal pale arc pops into view. It rapidly expands into a thin circular shell, then fades away as it fills the view. The whole thing takes a few minutes to expand; you can see the stars moving during the event (some of the pixels on the webcam are very sensitive and make stationary "hot spots" in the field of view).

So what is it? Is it a trans-dimensional portal into the future, some wormhole from the Pegasus galaxy, or two alien spaceships battling it out?

In point of fact, we are seeing something related to space war…

I first saw this video on Starship Asterisk, the discussion forum for the wildly popular Astronomy Picture of the Day website. The conversation there about this event is going pretty well, and I think this whole thing has been nailed down to a reasonable series of events. First, let’s look at a still frame from the video: